There is a large and competitive market for portable computers, and new and more powerful products are being rapidly developed. In these developments, a persistent design problem is that state-of-the-art microprocessors, which are desirable in these new systems, generate a considerable amount of waste heat. This heat buildup presents a design challenge, since the general trend in portable general-purpose computers is for smaller and lighter units. These smaller units are classified as subnotebooks.
Designers are now packing much of the same power and functionality of a full-sized notebook into a device measuring about 7 by 10 by 1.25 inches or less and weighing between two and four pounds. These two market trends of more powerful notebooks, reaching performance levels of desk-top computers, and smaller portable general-purpose computers, are defining future engineering efforts. Since there is typically no room for a fan in these products, notebooks must be engineered to dissipate heat passively to cool their components.
Presently, Intel Corporation's 486 line of microprocessors, as well as other manufacturers' devices, are being adapted for use within the close confines of notebook general-purpose computers. Intel's 486 family of CPUs contains 1.2 million transistors, three times as many as in the previous 386 series of CPUs. Heat is generated from millions of silicon transistors packed into smaller and smaller integrated circuits (ICs), switching on and off millions of cycles per second. This mechanism of switching on and off at the rate of the CPU, sometimes at frequencies as high as 66 Mhz, is a major factor in the generation of waste heat. A relatively large amount of work goes into alternating the voltage inside an IC's integrated bus. It is necessary for a semiconductor switch to electrically connect to either the power supply's positive or negative output and conduct a momentary but massive flow of electrons. The result is a charging or discharging of the electric potential that is stored in the circuit trace. Each time the IC wire trace's voltage is charged, a brief pulse of electron flow is typically conducted through the semiconductor switches,
A compounding of the problem of heat buildup occurs because the increasing thermal resistivity as temperature increases causes even more rapid heat buildup. The waste heat must be removed, otherwise the snowballing effect of more and more heat compromises the system performance.
More sophisticated software makes matters worse. IBM Corporation's OS/2.1.TM. and state-of-the-art UNIX operating systems already employ 32-bit processing, which uses a 486's intrinsic architecture fully. Meanwhile, Microsoft is preparing a new version of Windows, dubbed Windows NT, which will do the same. These operating system environments use the maximum data bandwidth to transfer information within the computer system. This leaves few circuits idle within the tightly configured CPUs, and thermal engineering parameters are therefore tested at maximum levels for maximum periods of time. Another technical development uses faster bus systems to link the faster CPUs to system peripherals. Rather than the slow input/output (I/O) speeds of 8 megahertz many desk-top and file server general-purpose computers are now using, newer systems employ Video Electronics Standards Association (VESA) Local Bus or Extended Industry Standard Architecture (EISA) technologies, and fast proprietary systems. These pathways and associated faster peripherals effectively transfer data at the full external speed of the system's microprocessor. This demands the full computational attention of the CPU to satisfy data-hungry devices such as video and disk controllers. The addition of faster bus systems increases the loads inside any CPU and the generation of peak waste heat needing to be removed from the immediate area.
Intel and other vendors have alerted microcomputer manufacturers in their service manuals to the operating temperature range of the 486 chips. The temperature limits for safe operation are between variously quoted, A typical safe range is given as between 32 and 185 degrees Fahrenheit. Intel suggests that manufacturers use extra cooling fans and heat sinks to maintain these temperatures. These suggestions are strongly directed to manufacturers of "slim-line" computers. Therefore many are incorporating into their microcomputers extra fans and/or heat sinks directly attached to the 486 CPU or wherever design constraints will allow for proper thermal cooling.
Thermal concerns in electronic packaging have reached the point where designers of general-purpose computers can no longer afford to treat the dissipation of waste heat as an afterthought. With faster and hotter-running generations of ICs on the way, a prudent approach to packaging at both the IC level and at system level is imperative, The CPU duty life and performance are critical considerations while running temperatures are close to upper specification limits. A military computer design rule-of-thumb says that for every 10 degrees Centigrade rise above maximum temperature specification the chip's reliability is cut in half. Manufacturers that don't address the thermal implications that directly affect data transfers within CPU clock speed parameters risk premature microprocessor failures or malfunctions. An overheated CPU can cause various problems, ranging from data corruption to the loss of file-allocation tables to the microprocessor shutting itself down, or even self-destruction in extreme cases.
Some manufacturers have introduced combination heat sinks and cooling fans that attach directly to the CPU, These devices are too bulky for portable general-purpose computers measuring 1/2 inch high. They have established manufacturing efforts to address the inherent waste heat generated by the present production technology levels of the 486 microprocessors. Manufacturers such as Dell.TM. Computers have already been shipping 486-based desk-top microcomputers with built-in coolers.
Intel Corporation and other semiconductor manufacturers face more challenges in developing new generations of high-performance microprocessors. Intel's new Pentium.TM. microprocessor is due to succeed the 486 family of microprocessors, and will produce significantly higher levels of waste heat. The Pentium CPU will generate as much as 16 watts just to run itself.
Intel has established a certification procedure with microcomputer manufacturers to qualify general-purpose computers for safe Pentium use. The Pentium fits in a 238-pin socket that is standard on a variety of microcomputers and will generate enough heat to melt or damage surrounding components if not properly cooled. Presently only 10% of the tested name brand microcomputers, none of which are portables, are expected to have enough cooling for full certification.
The present invention addresses these thermal restraints particularly pertaining to the future use of high-performance microprocessors in portable general-purpose computers. The use of the next generation "hot" microprocessors will be soon introduced into the confining environments of portable general-purpose computers. The primary engineering "hurdle" of properly controlling CPU waste heat in the faster CPUs must be overcome to have them installed successfully. What is needed is a means of removing CPU-generated waste heat economically and effectively within the even smaller confines of a portable computer, guaranteeing optimal processing performance, longevity and reliability.